Farallon plate

The Farallon plate was an ancient oceanic tectonic plate. It formed one of the three main plates of Panthalassa, alongside the Izanagi plate and the Phoenix plate, which were connected by a triple junction. The Farallon plate began subducting under the west coast of the North American plate—then located in modern Utah—as Pangaea broke apart and after the formation of the Pacific plate at the center of the triple junction during the Early Jurassic. It is named for the Farallon Islands, which are located just west of San Francisco, California.

Over time, the central part of the Farallon plate was subducted under the southwestern part of the North American plate. The remains of the Farallon plate are the Explorer, Gorda, and Juan de Fuca plates, which are subducting under the northern part of the North American plate; the Cocos plate subducting under Central America; and the Nazca plate subducting under the South American plate.^[1]

The Farallon plate is also responsible for transporting old island arcs and various fragments of continental crust, which have rifted off of other distant plates. These fragments from elsewhere are called terranes (sometimes, "exotic" terranes). During the subduction of the Farallon plate, it accreted these island arcs and terranes to the North American plate. Much of western North America is composed of these accreted terranes.